68 4 SECRETION AND ABSORPTION B Y THE SKIN. 



excitation of the nerves. The strength of the stimulus, and the extent to 

 which the normal ingoing " current of rest " is developed, affects the result, 

 and hypotheses have been based upon both of these factors of the case. 



Hermann l long ago suggested the possibility of augmenting and inhibitory 

 fibres to the glands, and in his most recent publication' 2 still entertains the 

 idea. On the other hand, Biedermann suggests that the two sides of protoplasmic 

 activity (the katabolic and anabolic) in the secretory cells are associated with 

 generation of electro-motive force, causing currents in opposite directions 

 in the two cases ; that the electro-motive force of the " current of rest " is 

 the algebraic sum of these opposing forces at the moment ; and that the results 

 of nerve excitation are related directly to the ascendancy of one or the other 

 metabolic action at the time of stimulation. 



The production of an outgoing "current of action" is considered by 

 Biedermann as due to the nerve excitation provoking an excess of anabolic action 

 in the cell, that of an ingoing " current of action " as due to excess of katabolism, 

 so that one and the same class of nerve-fibre is supposed to produce quite 

 opposite results in the cell, the effect being partly conditioned by the state of 

 the balance in the cell between the two processes at the moment of excitation, 

 and partly by the strength of the stimulus. He supposes that the cell process 

 least developed at the time of excitation, tends to be stimulated in excess of its 

 fellow, so that if the ingoing "current of rest" is weak, as a result of slight 

 katabolic ascendancy, excitation tends to cause an ingoing " current of action " ; 

 and, vice versa, if the ingoing " current of rest " is strong, as a result of marked 

 katabolic ascendancy, the result of excitation of the cell is liable to be the 

 development of an outgoing " current of action." 



Hermann objects to this, that if the electrical sign of excess of anabolism 

 over katabolism is plus, the induction of such a condition must start from the 

 deep ends of the cells, i.e. from the ends from which they get their pabulum 

 from the blood, and excess of positivity of this end of the cell comes, so far as 

 the direction of current is concerned, to the same thing as excess of negativity 

 at the free end of the cell, associated by hypothesis with katabolic ascendancy, 

 and should develop a current in the same direction, i.e. ingoing. 



It may also be noted in this connection, that, according to Bohlen, 3 in 

 the gastric mucosa of mammals, cessation of circulation or any interference 

 with blood supply tends to convert the normal ingoing into an outgoing 

 " current of rest." If an outgoing current is associated with excess of anabolism 

 over katabolism, it is difficult to conceive how withdrawal of blood supply can 

 induce such a change. A similar complete reversal of the direction of the 

 " current of rest " is obtainable in the secreting membranes of the frog and 

 fish by abstraction of heat, or by narcotisation with carbonic acid gas, ether, 

 or chloroform. 



A strong stimulus of a nerve trunk may, in practice, cause an outgoing 

 action current, and a weak stimulus one that is ingoing, but it is again difficult 

 to conceive that difference in the strength of stimulus of one class of nerve- 

 fibre can alter the whole character of the metabolism in the cells. 



Hermann was at one time of opinion that the two kinds of glands in the 

 frog's skin might be associated with the two phases of the excitatory variation ; 

 and the lip of the eel, which contains no club cells but only goblet cells, gives 

 an outgoing " action current," while the body skin, rich in club cells and poor in 

 goblets, gives an ingoing " action current " with the same strength of stimulus ; 4 

 but since the cloacal or pharyngeal mucosa of the frog, containing only one sort 

 of secretory cell, and the non-glandular crop of the winter pigeon, can give 

 currents in both directions, the hypothesis is not of universal application. 



1 Arch.f. d. ges. PhysioL, Bonn, 1878, Bd. xvii. S. 303. 



2 Ibid., 1894, Bd. Iviii. S. 242. 3 LOG. dt. 



4 Reid and Tolputt, Journ. PhysioL, Cambridge and London, 1894, vol. xvi. p. 203. 



